Open-heart surgery usually requires the use of a system for the extracorporeal circulation of fluids through a number of fluid circuits. These fluid circuits typically include a cardiopulmonary circuit, a cardioplegia circuit, a cardiotomy circuit and a ventricular vent circuit. The circuit tubing, pumps and related instrumentation and support console are referred to as a perfusion control system or a heart-lung machine.
The cardiopulmonary circuit, which is designed to functionally replace or supplement the heart and lungs during heart surgery, comprises one or more pumps for blood circulation and an oxygenation device. In prior art systems such as the COBE.RTM. Perfusion Control Assembly, a catheter receives blood from a major vessel entering the heart (e.g., vena cava) and the blood is directed through a venous line to a blood reservoir, through a cardiopulmonary loop to an oxygenator, and then back to the patient through an arterial line to a catheter in a major vessel leaving the heart (e.g., aorta). Either the arterial line or cardiopulmonary loop has a pump disposed thereon; the venous line may have a pump disposed thereon. It is generally desirable to have the cardiopulmonary circuit (both arterial and venous lines) be as short as safely possible to reduce priming volume and extracorporeal blood volume, blood dilution and inadequate oxygenation, and to minimize the need for transfusions and the attendant risk of blood-borne infections (e.g., HBV, HCV, or HIV). The cardiopulmonary pump on the cardiopulmonary loop or arterial line (sometimes referred to as the arterial pump) is used to pump blood from the reservoir through an oxygenation device. The reservoir is often positioned at a level below that of the patient on the operating table so as to permit gravitational drainage from the patient into the venous line. The blood is then pumped through an oxygenator and then an arterial line and another catheter into a major vessel exiting the heart. The cardiopulmonary circuit may include other devices such as a bubble detector on the arterial line to guard against bubbles entering the bloodstream; microemboli filters on the arterial line to prevent thromboemboli or gas emboli from entering the bloodstream; a timer to record the duration of extracorporeal blood circulation; temperature sensors and heat exchangers to monitor and control the temperature of the circulated blood; pressure transducers to monitor the pressure in the extracorporeal circuit; and devices to monitor blood characteristics such as the hemoglobin, oxygen saturation level, hematocrit, pH and blood gases. The cardiopulmonary pump can be a peristaltic, centrifugal, bladder or other pump, and it may be operable in a steady and continuous manner or in a pulsatile manner to mimic the beating of the heart.
The cardioplegia circuit delivers cardioplegia to the heart. Cardioplegia reduces or discontinues the beating of the heart in a manner that will minimize damage to the myocardium. Cardioplegia can also supply other ingredients to provide for myocardium protection. Cardioplegia may be the crystalloid solution (KCl, sugars, dextrose, magnesium, etc.) alone or may include oxygenated blood diverted from the arterial line. The cardioplegia circuit comprises the oxygenated blood line, the crystalloid solution bag and line, the cardioplegia delivery line, a pump (e.g., peristaltic), and may also comprise pressure transducers to monitor the solution pressure, an air detector and filters to prevent bubbles from entering the heart, a timer, temperature sensors and a heat exchanger to monitor and control fluid temperature, and a device for controlling and recording the total volume of crystalloid solution that is pumped. The cardioplegia is delivered to the coronary arterial network or coronary sinus for distribution throughout the myocardium. The cardioplegia is then distributed through the circulatory system, or may occasionally be drawn out of the chest cavity and discarded or directed via the cardiotomy line to the cardiopulmonary circuit, as discussed immediately below.
The cardiotomy circuit is used to withdraw or suction blood or blood mixed with other fluids from the opened heart or the chest cavity and deliver it to the cardiopulmonary circuit. The cardiotomy circuit typically comprises a suction tip, a fluid line, a pump (e.g., peristaltic), and a reservoir, and may comprise a filter disposed in the fluid line. The filter functions to remove foreign material picked up by the suction tip of the cardiotomy circuit. The cardiotomy reservoir may be the same as the cardiopulmonary blood reservoir. In addition to storing suctioned blood, the cardiopulmonary and cardiotomy reservoirs can also function to filter and defoam the blood.
The ventricular vent circuit functions to drain the left ventricle of blood that returns via the bronchial artery and pulmonary veins. Drainage from the pulmonary system, the coronary venous system and backflow from the aorta to the left ventricle can overfill the ventricles during bypass surgery. Such distention can stretch muscle fibers and weaken them. The ventricular vent circuit typically comprises a cardiac catheter inserted into the left ventricle, tubing, a pump (e.g., peristaltic), and a reservoir. The vent circuit reservoir may be combined with the cardiotomy and cardiopulmonary blood reservoirs.
In addition to the foregoing, auxiliary pumps may also be provided as back-up pumps in the event of failure of the cardiopulmonary, cardioplegia, cardiotomy or vent pumps during surgery.
Existing systems for extracorporeal circulation or perfusion systems are commonly mounted on a wheeled console for convenient storage, transport and use. The typical mounting configuration includes a vertical or horizontal row of discrete units. The units can be pump assemblies (cardiopulmonary, cardioplegia, cardiotomy, vent or auxiliary pump) or a controller unit. The pump assembly typically comprises a pump housing which contains the actual pumping elements, such as a rotor with a set of rollers to engage the flexible tubing through which the pumped fluid flows and a raceway to hold the flexible tubing in place, and the pump motor and other mechanical components. The pump assembly also may comprise an instrumentation panel which could include pump controls such as power switches, speed adjustments and indicators, and forward and reverse controls. The controller unit can monitor pressure and temperature probes, bubble sensors and reservoir level sensors, regulate pump speeds, and transmit monitored information to a display. Pump assembly and controller units can be detachable and modular.
The wheeled console commonly has a number of accessories and a structure for attachment of the accessories. The structure may include one or more vertical poles or masts, a mounting crossbar and brackets for hanging or attaching fluid reservoirs, accessory instrumentation (e.g., a display), writing surfaces, bubble detectors, temperature sensor readouts and other desired devices. The oxygenator is typically mounted on a mast or crossbar.
The physical arrangement of fluid lines, pumps, reservoir, oxygenator and other components of the fluid circuits is important for proper operation of the perfusion system. It is generally considered important to have an arrangement that reduces the extracorporeal volume of all blood-containing circuits so as to reduce the need for transfusion or dilution. Additionally, the physical arrangement should be such that the perfusionist can scan, take samples, and consistently be aware of the status of all equipment, systems, and patient parameters. Adjustment of ventilation gases and administration of drugs can be based on observations made by the perfusionist. Once cardiopulmonary bypass has begun, the perfusionist must observe and regulate pump flow rates, check the color of and pressure in the arterial line, observe the blood level in the reservoir(s) to assure a steady state or balanced flow in and out, observe tubing for air in the lines, leaks or kinking, and regulate heat exchanger temperature to induce system hypothermia to the desired level. It is highly desirable that the perfusionist be able to observe the surgical team and operating table, and to observe and have direct access to the oxygenator, the fluid lines, the pumps, the reservoirs, etc. from a single standing or sitting position. For example, if the perfusionist observes that the blood level in the cardiopulmonary reservoir is rising due to an excessive venous return, he can adjust a clamp on the venous return line to slow the blood flow into the extracorporeal circuit and stabilize the blood level in the reservoir. In another example, the perfusionist, upon observing or learning of the premature reinitiation of the patient's heart beat (i.e., prior to termination of open-heart surgery), may adjust the cardioplegia pump or a clamp on the cardioplegia delivery line to increase the crystalloid concentration to the heart.
Historically, i.e., in the 1950's, bubble oxygenators (membrane oxygenators were not invented until the 1960's) were located behind a console comprising cardioplegia and cardiopulmonary pumps. An example of this design is the Rygg-Kyvsgaard heart-lung machine manufactured by Polystan (described in Rygg, I. H. et al., "The Rygg-Kyvsgaard Pump-Oxygenator" in Ionescu, M. I. (1976) Current Techniques in Extracorporeal Circulation, Butterworth & Co., Great Britain). It was necessary to place the oxygenator behind the pumps because it was a large bag that could be extended only by mounting on a crossbar. The height of the oxygenator crossbar was adjusted to control the venous flow rate. Therefore, the oxygenator bag was often not completely visible to the perfusionist. The bubble or membrane oxygenators of the 1960's were smaller and the venous flow rate was controlled by a clamp on the venous line rather than by adjusting the height of the oxygenator. Consequently, the oxygenator was moved from behind the horizontal array of pumps to a peripheral position (i.e., to the left or right of the horizontal array) to improve accessibility and visibility. At this time there were still usually only two pumps located on the console. However, heart-lung machines became more complex over time with the addition of a cardiotomy pump, a ventricular vent pump, a central controller module, a display, temperature and pressure sensors, reservoirs, etc. By the 1970's, most manufacturers employed at least four pumps in a horizontal array with an oxygenator located peripherally. While the addition of new components to the perfusion control system improved its performance, such additions also increased the system's footprint, thereby creating perfusionist ergonomic issues. Specifically, the perfusionist would often have to shift positions to have access to each component of the system. Further, the larger footprint increased the perfusionist's routine visual circuit to monitor all components. For example, the perfusionist in some cases had to shift his stool or take one or more steps in order to obtain a clear view of a component. Thus, there has been a need since the 1970's for a perfusion assembly design that addresses these concerns. The expanding complexity of the heart-lung machine has been noted by skilled artisans in the field. See, e.g., Nose, Y. (1989) Artif. Organs 13:89-90; and Galletti, P. M. (1993) Artif. Organs 17:675-86.
As discussed above, one currently existing extracorporeal circulation or perfusion assembly is the COBE.RTM. Perfusion Control System (sold by the assignee of the subject application), which features a horizontal row of pump modules and the Perfusion Controller module on the console; and the oxygenator, display, air emboli protection system, venous line occluding clamp, gas flow meter and halogen console lamp fastened to the masts or mounting crossbar. As described in copending U.S. Ser. No. 07/941,389, now SIR H1324, incorporated herein in its entirety by reference, which describes an alternative control system for the COBE Perfusion System, the control of the pumps in the horizontal array (referred to in SIR H1324 as "perfusion assemblies") may be via the local instrumentation panel or the controller unit. The oxygenator is adjustable on the mast via a swing arm, and can be swung approximately 270.degree. about the mast axis from a position in which it is adjacent to an outside pump assembly in the horizontal array to a position where it is centrally located behind the horizontal row of modules. The latter position may reduce the length of the cardiopulmonary circuit, but frequently requires the perfusionist to move to obtain a clear view of the oxygenator and access for clamping or debubbling.
Other currently existing systems include the Sorin SIII.TM. Perfusion System, the Sarns.RTM. 8000 Perfusion System, the Polystan.TM. Heart-Lung Machine System, the Pemco.TM. system, and the Bard.RTM. Cardiopulmonary Support (CPS.TM.) System. The Sorin Perfusion System also features a horizontal row of pump modules on the console, with a halogen console light, venous occlusion clamp and instrument stack for control and monitoring modules mounted on masts or mounting crossbars. The Sarns 8000 Perfusion System has a horizontal arrangement of its pumps, display, monitoring and control functions. The Polystan Heart-Lung Machine System comprises a horizontal row of pumps on a console, a horizontal modular monitoring rack mounted at eye level (which appears to obstruct a view of the operating table), a computer interface and communications port in its console base, masts or I.V. poles, and an IBM compatible program which collects and displays data accumulated from the monitors. The Pemco heart pump console can be customized to provide a horizontal or vertical arrangement of modular pumps. In the Sorin, Sarns, Pemco and Polystan systems, the oxygenator is peripherally mounted on a mast. The Bard cardioPulmonary Support system, which is designed for cardiopulmonary support in emergency situations, comprises an oxygenator centrally located between a pump and a heat exchanger.